1. Field of the Invention
This invention relates to cutter chains having picks and to picks therefor.
2. Prior art
It is well known to use a continuously driven endless cutter chain formed of pick boxes carrying picks for cutting rock and for mining. Such a cutter chain may be used for example in a trench cutter, the cutter chain being mounted on a chain carrier which is lowered into the ground. The chain may be driven at a high speed for example more than 300 ft per minute and one of the problems with such cutter chains is the tendency of the pick to kick backwards as it cuts through strata of varying hardness and density. Thus a pick may be driven in a direction tending to dig deeply into the rock; this may result in the pick breaking or the chain stalling. For this reason, it is known to provide each pick box with a back stop limiting angular movement about an axis transverse to the plane of the endless chain. However the continuous peening action during operation on the stops on the pick boxes in such an arrangement results in the gradual change in the effective position of the stop and, since the angle of attack of the pick is critically dependent on the stop position, it is necessary that the pick boxes should be periodically replaced. This results in a very considerable increase in the maintenance work required on such cutter chains.